1. Field of the Invention
The present invention pertains to digital imaging. More particularly, this invention relates to generating a high resolution scan image with a low resolution scan sensor, wherein the high resolution scan image is generated by generating additional multiple tilted scan lines using the low resolution scan sensor which requires no accurate movement of the scan sensor.
2. Description of the Related Art
It has been known that when an original image (i.e., an image rendered on a physical medium such as paper) is scanned by a scanner, a digital image of the original image is generated. Examples of the original image include photos and text/graphics documents. FIG. 1 is a perspective view of a prior art flatbed scanner 10. As can be seen from FIG. 1, the scanner 10 includes a housing 11 and a scan window 12, on which an original image can be placed for the scanner 10 to generate the corresponding digital image. The structure of the scanner 10 inside the housing 11 is schematically illustrated in FIG. 2.
As can be seen from FIG. 2, the scanner 10 is typically structured such that the original image 21 is illuminated by light from an light source (not shown) and the light reflected from the original image 21 is detected by a sensor 14 having an array of imaging elements (e.g., Charge Coupled Devices) to generate a number of scan lines, one scan line at a time. Each scan line includes a number of image pixels (e.g., the image pixels 33 through 33n in FIG. 3). The scan sensor 14 generates a scan line at one time. Then the scan sensor 14 advances in the scan direction to generate the next scan line. The control circuit 15 controls the movement of the scan sensor 14 to generate the scan lines.
The scan lines are sent to a control circuit 15 of the scanner 10 where the scan lines are assembled or constructed into a scan image 30 (see FIG. 3). The scan image 30 typically includes a digital image 31 of the original image 21 as well as background information. The scan image 30 is then cropped to obtain the digital image 31 without background image pixels. The digital image 31 can then be stored electronically, for example, in a computer system. The digital image 31 can also be electronically displayed and printed by a printer.
As is known, it is typically more desirable to view a high resolution scan image as it is typically clearer and reveals more details than a low resolution scan image. Using a low resolution sensor typically causes many fine image details to be imaged between the imaging elements of the sensor. This typically causes the resultant scan image to lose these fine details, thus causing the scan image to be more blurred and coarse.
The image resolution of a scan image is determined by two factors. One is the pixel distance between any two adjacent image pixels within a scan line (i.e, the scan density or imaging density). As can be seen from FIG. 3, the number of image pixels for each scan line corresponds to the number of the imaging elements within the sensor 14. The more imaging elements within the sensor 14, the shorter distance between any two image pixels and the higher image resolution of each scan line.
The other factor that determines the image resolution of a scan image is the scan advance distance between any two scan lines. As can be seen from FIG. 3, this distance determines the gap or space between any two adjacent scan lines. This scan distance is created when the sensor completes one scan line and advances to create the next scan line. The smaller this scan distance, the higher image resolution the scan image.
One prior art approach to increasing the image resolution of a scan image is to increase the imaging density of the sensor. As is known, the ideal imaging density for a sensor is that all the image elements of the sensor are aligned next to each other without any gap or space in between. However, it is almost impossible to fabricate a sensor with the-above mentioned ideal imaging density. Gap or space is required between any two adjacent image elements to prevent interferences. In addition, it is relatively difficult to manufacture high density image sensors as the manufacturing process typically requires significantly higher degree of precision. Moreover, such a high density image sensor is typically very costly to produce.
Another prior art approach to increasing the image resolution of a scan image is to reduce the scan distance between the scan lines. Using this prior art approach, the scan distance between any two adjacent scan lines is reduced such that more scan lines can be produced for the scan image. Here, the scan lines continue to remain parallel with one another. One disadvantage of this approach is that misalignment of the sensor may occur when the scan distance is made very small. Misalignment means that two adjacent scan lines are either completely overlapped or partially overlapped. Time, operation environment, and changes in device parameters all may contribute to misalignment when the scan distance is made very small. Very high level of precision control of the sensor movement are typically required to prevent misalignment, which can be very costly and sometimes impossible to accomplish.
One feature of the present invention is to increase image resolution of a scan image.
Another feature of the present invention is to increase image resolution of a scan image cost effectively.
A further feature of the present invention is to produce a scan image with high image resolution using a low resolution scanner without requiring precise movement of the scan sensor.
An image scanning apparatus is described that includes a sensor having an array of predetermined imaging elements to generate a plurality of scan lines of image pixels from an original image. The image scanning apparatus also includes a control module that controls the sensor to generate the scan lines, some of the scan lines are tilted with respect to other scan lines such that at least some image pixels of any two adjacent lines are not overlapped. An imaging module is also provided in the image scanning apparatus that generates a scan image from the scan lines such that image resolution of the scan image is increased without increasing scan resolution of the sensor.
In one embodiment, the control module controls the sensor to first generate the non-tilted scan lines and then controls the sensor to generate the tilted scan lines. In another embodiment, the control module controls the sensor to alternately generate the non-tilted scan lines and the tilted scan lines.
A method of enhancing image resolution of a scan image using a low scan resolution scanner is described. The method includes the step of generating a plurality of scan lines of image pixels from an original image using a scan sensor having an array of predetermined imaging elements. Some of the scan lines are tilted with respect to other scan lines such that some image pixels of any two adjacent lines are not overlapped. The method then generates the scan image from the scan lines such that image resolution of the scan image is increased without increasing the scan resolution of the sensor. The scan image is generated by processing the scan lines to collect and filter redundant information from the scan image.
In one embodiment, the method first generates the non-tilted scan lines and then the tilted scan lines. In another embodiment, the method alternately generates the non-tilted scan lines and the tilted scan lines.
Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.